: Progress has been made in understanding long-term potentiation (LTP) in the CA1 region of hippocampus, but the molecular basis of the underlying storage mechanism remains unclear. Several lines of evidence support the hypothesis that synaptic memory is maintained by postsynaptic CAM-kinase or C-kinase: postsynaptic application of either kinase can enhance synaptic responses and biochemical data indicate that LTP causes persistent activation of both kinases. To further study the role of these kinases in the maintenance of LTP, several further tests will be conducted using the whole cell recording method in the slice preparation. Activated C-kinase or CaM-kinase will be introduced into the cytoplasm using the perfused patch pipette method. Previous work has shown that either kinase can enhance synaptically evoked responses. The investigators will determine whether there is occlusion between the enhancement produced by exogenous kinase and the enhancement produced by LTP, as would be expected if they work by the same mechanisms. To determine whether persistent kinase activity is required for the maintenance of LTP, inhibitors of the kinases will be introduced after LTP induction. As a prelude to these experiments, the concentration of inhibitor required to reduce the effect of exogenous kinase will be determined. After the effectiveness and specificity of inhibitors is established in this way, their ability to block or not block pre-established LTP becomes a strong test of the role of kinases in LTP maintenance. A second goal of the proposal is to study the role of postsynaptic phosphatases in synaptic plasticity. The ability to reversibly introduce phosphatase inhibitors into the postsynaptic cell makes it possible to test whether disruption of the balance between phosphatase and kinase enables the LTP switch to be thrown by purely postsynaptic manipulations. In a final set of experiments, purified phosphatases will be perfused into the postsynaptic cell. The experiments are aimed at determining how phosphatases affect the synaptic response and how they contribute to the activity-dependent weakening of synapses.